Artificial dielectric material and method of manufacturing the same

ABSTRACT

An artificial dielectric material comprising a plurality of blocks of dielectric material, each block have at least one conductive fibre or wire embedded within. A method of making the material is disclosed where a plurality of strands or wires are embedded in dielectric layer which is then chopped in blocks. These blocks then fall randomly into a container in any order or pattern and are glued into a solid layer.

FIELD OF INVENTION

The present invention relates to an artificial dielectric material and amethod of manufacturing the same.

BACKGROUND

Artificial dielectric material mixed with randomly distributedconductive fibres is a well-known composition.

However, various problems exist affecting dielectric losses inconventional artificial dielectric material mixed with randomlydistributed conductive fibres. FIG. 1 (Prior Art) illustrates randomlydistributed conductive fibres 102 in a conventional artificialdielectric material. As shown in FIG. 1, the distribution of the fibresin the material is not uniform, some parts of the material consist ofmore conductive fibres than other parts. Also, after mixing, someconductive fibres make contact with one another to create conductiveclusters 104. Each cluster may consist of a different number of fibres.The overall effect of fibres and other fibres or clusters havingdifferent distances apart and non-uniform concentrations of fibres is anincrease in dielectric losses in the material.

In the complex representation of the permittivity of a dielectricmaterial, ∈″ represents the imaginary part of the permittivity of thematerial, which is related to the rate at which energy is absorbed bythe material (converted into thermal energy, etc.). Hence, ∈′ is ameasure of dielectric losses in a dielectric material. The response ofdielectric materials to external electromagnetic fields generallydepends on the frequency of the field. In order to achieve small losses(i.e. small ∈″) at a required frequency for dielectric material mixedwith conductive fibres, it is necessary that the length of the fibres inthe dielectric material be much smaller compared to the wavelength atthe required the frequency.

The creation of clusters affects uniformity, anisotropy, and increasesthe dielectric losses of the material by increasing the resonance widthof ∈″. When fibres make contact with each other, it is equivalent toincreasing the length of the fibres. This increase in length undesirablyleads to the shifting of resonance losses to a wide frequency range, inparticular, the lower frequency range. In addition, with fibres andclusters having different distances apart, the frequency width ofresonance losses is further increased. All these problems also lead tothe amplification of dielectric losses in a wide frequency band, inparticular, the lower frequency range, and can affect the fabrication ofdielectric materials for devices such as dielectric lenses, dielectricantennas etc.

Conventionally, low loss dielectric materials for instance, solid blocksof polystyrene, polyethylene, or the like, in use are relatively heavyin weight. For some applications of the dielectric materials, such asdielectric antennas, being heavy is considered an undesirable feature.

A need therefore exists to provide an artificial dielectric materialthat addresses at least one of the above-mentioned problems.

SUMMARY

In accordance with one aspect of the present invention, there isprovided an artificial dielectric material comprising: a plurality ofparticles adhered together, the plurality of particles comprising adielectric material; and at least one conductive fibre embedded in eachparticle of the plurality of particles.

The plurality of particles may be adhered together using a rubberadhesive or an adhesive comprising of a material in a group consistingof: polyurethane; and epoxy.

The plurality of particles may be randomly distributed in the artificialdielectric material.

The dielectric material may have a density in the range of 0.005 to 0.1g/cm³.

The dielectric material may be a foam polymer.

The foam polymer may be made of a material in a group consisting of:polyethylene; polyestyrene; polytetrafluoroethylene (PTEF);polypropylene; polyurethane; and silicon.

The average end-to-end measurement of each particle of the plurality ofparticles may be in the range of 0.5 to 5 mm.

Each particle of the plurality of particles may be substantiallycube-shaped. Each conductive fibre may be substantially needle shaped.

The conductive fibre may have a length in the range of 0.5 to 5 mm and adiameter in the range of 0.005 mm to 1 mm.

The at least one conductive fibre may be made of a material in a groupconsisting of: Copper; Aluminium; Nickel; Silver; and Gold.

Each particle of the plurality of particles may comprise at least twoconductive fibres arranged in an array.

The at least two conductive fibres may be arranged parallel to oneanother.

The array may comprise 1 to 10 rows.

The array may comprise 1 to 10 columns.

The at least two conductive fibres may be oriented such that theconductive fibres in one row are parallel to the conductive fibres inanother row.

The at least two conductive fibres may be oriented such that theconductive fibres in one row are transversely disposed with respect tothe conductive fibres in another row.

The at least two conductive fibres may be oriented such that theconductive fibres in one column are parallel to the conductive fibres inanother column.

The at least two conductive fibres may be oriented such that theconductive fibres in one column are transversely disposed with respectto the conductive fibres in another column.

The at least two conductive fibres may be evenly spaced apart.

The at least two conductive fibres may be randomly spaced apart.

Different dielectric materials may be used for different particles inthe artificial dielectric material.

Different materials may be used for the conductive fibres in a firstparticle and the conductive fibres in a second particle in theartificial dielectric material.

In accordance with another aspect of the present invention, there isprovided a method of manufacturing an artificial dielectric material,the method comprising: embedding at least one conductive fibre in eachparticle of a plurality of particles, the plurality of particlescomprising a dielectric material; and adhering together the plurality ofparticles to form the artificial dielectric material.

The step of embedding at least one conductive fibre in each particle ofthe plurality of particles may comprise stacking one or more rows ofconductive fibres in parallel arrangement and two or more sheets of thedielectric material such that each row of conductive fibres in parallelarrangement is disposed between at least two sheets of the dielectricmaterial.

The method may further comprise cutting the stacked rows of conductivefibres and sheets of the dielectric material to produce the plurality ofparticles.

The method may further comprise mixing the plurality of particles sothat the particles are randomly distributed in the formed artificialdielectric material.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be better understood and readilyapparent to one of ordinary skill in the art from the following writtendescription, by way of example only and in conjunction with thedrawings, in which:

FIG. 1 (Prior Art) illustrates randomly distributed conductive fibres ina conventional artificial dielectric material.

FIG. 2 illustrates random orientation of a multitude of particles in anartificial dielectric material according to an example embodiment.

FIG. 3 illustrates results of measurements of transmission coefficientvs frequency for an empty waveguide, a waveguide filled with theartificial dielectric material of the example embodiment illustrated inFIG. 2 and a waveguide filled with a conventional artificial dielectricmaterial.

FIG. 4 shows a particle in an artificial dielectric material accordingto an example embodiment.

FIG. 5 shows a particle in an artificial dielectric material accordingto an alternate example embodiment.

FIG. 6 shows a particle in an artificial dielectric material accordingto another alternate example embodiment.

FIG. 7 shows the frequency dependence of the dielectric permittivity ofan artificial dielectric material composed of the particle illustratedin FIG. 6.

FIG. 8 shows a particle in an artificial dielectric material accordingto another alternate example embodiment.

FIG. 9 shows the frequency dependence of the dielectric permittivity ofan artificial dielectric material composed of the particle illustratedin FIG. 8.

FIG. 10 shows the steps involved in the process of manufacturing anartificial dielectric material according to an example embodiment.

FIG. 11 shows the steps involved in the process of manufacturing anartificial dielectric material according to another example embodiment.

DETAILED DESCRIPTION

An artificial dielectric material according to example embodiments ofthe present invention is lightweight, irrespective of its dielectricconstant, and has low dielectric losses.

The artificial dielectric material of the example embodiments can bemade from a plurality of randomly distributed particles adheredtogether. The plurality of randomly distributed particles is made of alightweight dielectric material. The range of densities of thelightweight dielectric material can be 0.005 to 0.1 g/cm³.

At least one needle-like conductive fibre is embedded within eachparticle. Where there are at least two conductive fibres embedded withineach particle, the at least two conductive fibres are in an array likearrangement, i.e. having one or more row that include the conductivefibres. All the conductive fibres embedded within each particle are notin contact with one another.

In the example embodiments, each particle is represented as a cube.However, it is appreciated that the shape may vary in the actualimplementation.

Advantageously, the distribution of the conductive fibres is uniform asevery particle making up the artificial dielectric material of eachexample embodiment is substantially identical, that is, they include thesame number of conductive fibre(s). Furthermore, as each particle embedsthe conductive fibres in an array-like arrangement without allowing anycontact between the conductive fibres, conductive clusters are preventedfrom occurring. This advantageously results in reduction of dielectriclosses. The array-like arrangement can be a 1, 2, or 3 dimensionalarray.

In the example embodiments, the conductive fibres in array-likearrangement in one particle are randomly oriented with respect to theconductive fibres in array-like arrangement in another particle.

It is appreciated that the conductive fibres may be fully embeddedwithin each particle to prevent exposed tips of conductive fibres in oneparticle from contacting exposed tips of conductive fibres within otherparticles. However, it is also acceptable even if the tips are exposed.While, it is possible to have tip to tip contact in this case, theprobability of such contact is still significantly smaller than thecontact of randomly mixed fibres to form clusters in the methods ofconventional manufacturing of artificial dielectric materials asdescribed previously.

FIG. 2 illustrates an artificial dielectric material 200 according toone example embodiment. The plurality of identical particles 202 in theartificial dielectric material 200 is randomly oriented. There are 4conductive fibres 204 embedded in each particle 202 in the artificialdielectric material 200. The array arrangement of the 4 conductivefibres 204 is two by two, i.e. 2 rows and 2 columns of 4 evenly spacedconductive fibres in parallel arrangement with one another. In theembodiment, the length of each fibre can be about 1.5 mm and the size ofeach particle is about 1.5×1.5×1.5 mm. The particles can be made of alow-density polyethylene foam.

FIG. 3 illustrates empirical results of measurements of transmissioncoefficient 302 vs frequency 304 for firstly, a hollow rectangularwaveguide with a size of width, 10 mm, thickness, 23 mm and a length of400 mm (curve 1, 310), secondly, the same waveguide filled with theartificial dielectric material 200 (FIG. 2) (curve 2, 306), and thirdly,the same waveguide filled with a dielectric material having randomlymixed conductive fibres (curve 3, 308).

The dielectric material used to generate curve 3, 308, has the samenumber, type and length of conductive fibres and the same volume oflow-density polyethylene foam as the artificial dielectric material 200.The difference is in the method of manufacturing. The dielectricmaterial used to generate curve 3, 308 is manufactured by randomlymixing the conductive fibres with low-density polyethylene foam, as isdone conventionally. On the other hand, the method used formanufacturing the artificial dielectric material 200 ensures that eachparticle only consists of the same number of conductive fibres in anon-contact array-like arrangement.

The value of the transmission coefficient is a direct illustration ofthe dielectric losses in materials. The results in FIG. 3 showsignificant improvement of performance for the same waveguide filledwith the artificial dielectric material 200 (curve 2, 306) over theperformance of the same waveguide filled with dielectric materialshaving randomly mixed conductive fibres (curve 3, 308).

By observing curve 2, 306, and curve 3, 308, in FIG. 3, one can see thatthe difference in the transmission coefficient values between the twocurves increases with frequency. When comparing curve 1, 310, and curve2, 306, one can see that curve 2, 306, has small losses (i.e. less than0.5 dB) up to the frequency of 10 GHz (wavelength 30 mm). In contrast,when comparing curve 1, 310, and curve 3, 308, the losses up to thefrequency of 10 GHz is on average about 5 dB.

The particles in the example embodiments of the present invention aremade using a low-density and lightweight material. For instance, foampolymers made of polyethylene, with a typical density around 0.01 to0.02 g/cm³. It is appreciated that other foam polymers made ofmaterials, such as polystyrene, polytetrafluoroethylene (PTEF),polypropylene, polyurethane silicon, or the like, may be used to makethe particles.

The size of each particle in an example embodiment may be set at about1/20 of the wavelength of the selected operating frequency. Hence, at anoperating frequency of 10 GHz, particles about the size of 1.5×1.5×1.5mm are used. It is appreciated that the average end-to-end measurementof particle size, for any shape the particle may take, can be in therange of about 0.5 to 5 mm.

It is appreciated that the fibre length may be in the range of about 0.5to 5 mm depending on the operating frequency, and the diameter of eachconductive fibre may range from 0.005 to 1 mm. To further reduce theweight of the material, conductive fibres with smaller diameter may beused subject to the limitation that the skin depth at the operatingfrequency must be much smaller than the fibre diameter.

The embedded conductive fibres in the particles can be made from highlyconductive materials, for instance, copper, silver, gold, aluminium,nickel or the like.

Different configurations of the array like arrangement of the conductivefibres in each particle can achieve different dielectric constants forthe material. To achieve higher values of the dielectric constant, thenumber of fibres in each particle is increased. Conversely, to achievelower values of the dielectric constant, the number of fibres in eachparticle is reduced.

In the array like arrangement of the example embodiment, each row of thearray consists of a row of conductive fibres arranged in parallel to oneanother. Each row can include different number of fibres that are evenlyor randomly spaced apart. The distance between the fibres in adjacentrows can also be evenly or randomly spaced apart.

The fibres in different rows of the array can be oriented such that thefibres in one row are in parallel or transversely disposed (forinstance, arranged perpendicularly) with respect to the fibres inanother row.

In another embodiment, each column of the array can include a column ofconductive fibres arranged in parallel to one another. Each column caninclude different number of fibres that are evenly or randomly spacedapart. The distance between the fibres in adjacent columns can also beevenly or randomly spaced apart.

The fibres in different columns of the array can be oriented such thatthe fibres in one column are in parallel or transversely disposed (forinstance, arranged perpendicularly) with respect to the fibres inanother column.

It is appreciated that the number of fibres in each row and column mayrange from 1 to 10 or beyond. In one embodiment, each particle can havea 10×10 array of conductive fibres having 10 rows and 10 columns.

Some configurations illustrating the array like arrangement of theconductive fibres are herein described with reference to FIGS. 4 and 5.

FIG. 4 shows one embodiment of a particle 400 that includes a single rowarray of three needle-like conductive fibres 402.

FIG. 5 shows a particle 500 that includes four rows of fibres 502, 504,506 and 508. In this end, each row can include two evenly spaced fibresin a parallel arrangement. The second row 504 and fourth row 508 areoriented such that their conductive fibres are substantiallyperpendicular to the first row 502 and the third row 506.

The properties and frequency dependence of the different configurationsof the artificial dielectric materials according to the exampleembodiments is herein described with reference to FIGS. 6 to 9.

FIG. 6, illustrates a particle residing in an alternate embodiment ofthe present invention.

The particle 600 has a size of about 1.5×1.5×1.5 mm and is made of afoam-type expanded polyethylene with a density of about 20 kg/m³. Thenumber of rows 602 is 1. The number of conductive fibres 604 in each rowis 2. The distance between adjacent conductive fibres is about 1 mm. Thelength of each conductive fibre is about 1.5 mm and the diameter of eachconductive fibre is about 0.025 mm. The material used for the conductivefibres is copper.

An artificial dielectric material created by randomly mixing together aplurality of particles 600 has a density of about 51 kg/m³. At anoperating frequency of about 10 GHz, the real part of the dielectricpermittivity of the material, ∈′, is 1.25. The imaginary part of thedielectric permittivity, ∈″, (i.e. dielectric losses) is less than0.001.

The frequency dependence of the dielectric permittivity of the resultantdielectric material composed of the particle 600 in FIG. 6 isillustrated in FIG. 7. FIG. 7 shows a plot of dielectric permittivity702 vs frequency (GHz) 704. As one can see from FIG. 7, the real part ofthe dielectric permittivity is almost constant at frequency band 2-18GHz. The imaginary part of dielectric permittivity ∈″ has a small valueof approximately 0.001 at 10 GHz and is barely visible in the figure.

FIG. 8, illustrates a particle 800 residing in another alternateembodiment of the present invention.

The particle 800 has a size of about 1.5×1.5×1.5 mm and is made of afoam-type expanded polyethylene with a density of about 20 kg/m³. Thenumber of array rows 802 is 2. The number of conductive fibres 804 ineach array row is 4. The distance between adjacent conductive fibres isabout 0.3 mm. The length of each conductive fibre is about 1.5 mm andthe diameter of each conductive fibre is about 0.025 mm. The materialused for the conductive fibres is copper.

An artificial dielectric material created by randomly mixing together amultitude of particles 800 has a density of about 68 kg/m³. At anoperating frequency of 10 GHz, the real part of the dielectricpermittivity of the material, ∈′, is 1.46. The imaginary part of thedielectric permittivity, ∈″, (i.e. dielectric losses) is less than0.001.

The frequency dependence of the dielectric permittivity of the resultantdielectric material composed of the particle 800 in FIG. 8 isillustrated in FIG. 9. FIG. 9 shows a plot of dielectric permittivity902 vs frequency (GHz) 904. As one can see from FIG. 9, the real part ofthe dielectric permittivity is almost constant at frequency band 2-18GHz. The imaginary part of dielectric permittivity £″ has a small valueof approximately 0.001 at 10 GHz and is barely visible in the figure.

FIG. 10 is a flowchart 1000 illustrating a method for manufacturing anartificial dielectric material according to an example embodiment of thepresent invention. At step 1002, at least one conductive fibre isembedded in each particle of a plurality of particles, wherein theplurality of particles comprises a dielectric material. At step 1004,the plurality of particles is adhered together to form the artificialdielectric material.

In another example embodiment, the process of manufacturing theartificial dielectric material involves the following steps, as shown inFIG. 11.

At step 1102, copper wires of similar length and diameter in parallelarrangement are embedded in between sheets of foam-type expandedpolyethylene. Each row of conductive fibres in parallel arrangement isdisposed in between at least two sheets of the foam-type expandedpolyethylene. Firstly, a sheet of foam-type expanded polyethylene isplaced in position to form a base layer. Next, a row of copper wires inparallel arrangement is placed over and adhered to the top surface ofthe base layer. Thereafter, another sheet of foam-type expandedpolyethylene is placed over and adhered to the exposed copper wires soas to cover the exposed copper wires. If more than one row of copperwires is desired, more rows of copper wires and sheets of foam-typeexpanded polyethylene can be stacked one on top of the other in thesimilar fashion. At this step, the user can decide on the material touse for the wires and the lightweight dielectric material, the number ofrows of copper wires desired and the orientation of each row of copperwires. The thickness of the lightweight dielectric material and thedistance between the parallel copper wires can also be adjusted.

To achieve particles as described in FIG. 5, five sheets of foam-typeexpanded polyethylene are used to sandwich four rows of copper wirestherebetween. The sheets of foam-type expanded polyethylene and rows ofwires are stacked in the manner described above. Adjacent rows of thefour rows of wires would be deliberately placed perpendicular to oneanother.

To achieve particles as described in FIG. 8, three sheets of foam-typeexpanded polyethylene are used to sandwich two rows of copper wirestherebetween. Adjacent rows of the four rows of wires would bedeliberately placed parallel to one another.

After stacking the sheets in step 1102 to achieve the desired particledesign, the stacked sheets are cut using suitable tools and machinery toproduce the particles at step 1104.

At step 1106, all the particles produced in step 1104 are mixedrandomly.

At step 1108, the randomly mixed particles in step 1106 are coated withan adhesive and allowed to dry. The dried mixture forms a solidartificial dielectric material. The solid artificial dielectric materialmay be cut or further adhered together to form various sizes for use indifferent applications.

Examples of the type of adhesive used in the process are rubberadhesives or adhesives consisting of polyurethane, epoxy or the like,which have low dielectric losses.

Depending on the application of the dielectric material, it isappreciated that different materials may be used for different particlesin the same artificial dielectric material according to the exampleembodiments.

It is also appreciated that different materials may be used for theconductive fibres in one particle and the conductive fibres in anotherparticle in the same artificial dielectric material according to theexample embodiments.

Examples of some applications for the artificial dielectric materialaccording to the example embodiments are microwave lenses and dielectricantennas.

It will be appreciated by a person skilled in the art that numerousvariations and/or modifications may be made to the present invention asshown in the specific embodiments without departing from the spirit orscope of the invention as broadly described. The present embodimentsare, therefore, to be considered in all respects to be illustrative andnot restrictive.

1-27. (canceled)
 28. An artificial dielectric material comprising: aplurality of particles adhered together, the plurality of particlescomprising a dielectric material; and at least one conductive fibreembedded in each particle of the plurality of particles.
 29. Theartificial dielectric material as claimed in claim 28, wherein theplurality of particles are adhered together using a rubber adhesive oran adhesive comprising of a material in a group consisting of:polyurethane; and epoxy.
 30. The artificial dielectric material asclaimed in claim 28, wherein the plurality of particles is randomlydistributed in the artificial dielectric material.
 31. The artificialdielectric material as claimed in claim 28, wherein the dielectricmaterial has a density in the range of 0.005 to 0.1 g/cm³.
 32. Theartificial dielectric material as claimed in claim 28, wherein thedielectric material is a foam polymer.
 33. The artificial dielectricmaterial as claimed in claim 32, wherein the foam polymer is made of amaterial in a group consisting of: polyethylene; polyestyrene;polytetrafluoroethylene (PTEF); polypropylene; polyurethane; andsilicon.
 34. The artificial dielectric material as claimed in claim 28,wherein an average end-to-end measurement of each particle of theplurality of particles is in the range of 0.5 to 5 mm.
 35. Theartificial dielectric material as claimed in claim 28, wherein eachparticle of the plurality of particles is substantially cube-shaped. 36.The artificial dielectric material as claimed in claim 28, wherein eachconductive fibre is substantially needle shaped.
 37. The artificialdielectric material as claimed in claim 28, wherein the conductive fibrehas a length in the range of 0.5 to 5 mm and a diameter in the range of0.005 mm to 1 mm.
 38. The artificial dielectric material as claimed inclaim 28, wherein the at least one conductive fibre is made of amaterial in a group consisting of: Copper; Aluminium; Nickel; Silver;and Gold.
 39. The artificial dielectric material as claimed in claim 28,wherein each particle of the plurality of particles comprises at leasttwo conductive fibres arranged in an array.
 40. The artificialdielectric material as claimed in claim 39, wherein the at least twoconductive fibres are arranged parallel to one another.
 41. Anartificial dielectric material as claimed in claim 39, wherein the arraycomprises 1 to 10 rows.
 42. An artificial dielectric material as claimedin claim 39, wherein the array comprises 1 to 10 columns.
 43. Theartificial dielectric material as claimed in claim 39, wherein the atleast two conductive fibres are oriented such that the conductive fibresin one row are parallel to the conductive fibres in another row.
 44. Theartificial dielectric material as claimed in claim 39, wherein the atleast two conductive fibres are oriented such that the conductive fibresin one row are transversely disposed with respect to the conductivefibres in another row.
 45. The artificial dielectric material as claimedin claim 39, wherein the at least two conductive fibres are orientedsuch that the conductive fibres in one column are parallel to theconductive fibres in another column.
 46. The artificial dielectricmaterial as claimed in claim 39, wherein the at least two conductivefibres are oriented such that the conductive fibres in one column aretransversely disposed with respect to the conductive fibres in anothercolumn.
 47. The artificial dielectric material as claimed in claim 39,wherein the at least two conductive fibres are evenly spaced apart. 48.The artificial dielectric material as claimed in claim 39, wherein theat least two conductive fibres are randomly spaced apart.
 49. Theartificial dielectric material as claimed in claim 28, wherein differentdielectric materials are used for different particles in the artificialdielectric material.
 50. The artificial dielectric material as claimedin claim 28, wherein different materials are used for the conductivefibres in a first particle and the conductive fibres in a secondparticle in the artificial dielectric material.
 51. A method ofmanufacturing an artificial dielectric material, the method comprising:embedding at least one conductive fibre in each particle of a pluralityof particles, the plurality of particles comprising a dielectricmaterial; and adhering together the plurality of particles to form theartificial dielectric material.
 52. The method as claimed in claim 51,wherein the step of embedding at least one conductive fibre in eachparticle of the plurality of particles comprises: stacking one or morerows of conductive fibres in parallel arrangement and two or more sheetsof the dielectric material such that each row of conductive fibres inparallel arrangement is disposed between at least two sheets of thedielectric material.
 53. The method as claimed in claim 52, furthercomprising: cutting the stacked rows of conductive fibres and sheets ofthe dielectric material to produce the plurality of particles.
 54. Themethod as claimed in claim 51, further comprising: mixing the pluralityof particles so that the particles are randomly distributed in theformed artificial dielectric material.